1. Technical Field
The present invention relates to a piezoelectric vibrator element and a piezoelectric vibrator, and in detail to an excitation electrode for exciting a vibrating arm part.
2. Related Art
For example, in the electronic apparatus such as a cellular phone or a portable information terminal, there is used a piezoelectric vibrator using a quartz crystal or the like as a device used for a clock time source, a timing source for a control signal and so on, a reference signal source, and so on.
As a piezoelectric vibrator of this kind, there has been known a device having a piezoelectric vibrator element hermetically encapsulated in a cavity formed of a package and a lid member as shown in JP-A-2005-81501.
FIGS. 6A and 6B show the structure of a typical piezoelectric vibrator element 600 of related art, wherein FIG. 6A shows a perspective view, and FIG. 6B shows a perspective view viewed from the P-P cross-section.
As shown in FIGS. 6A and 6B, the piezoelectric vibrator element 600 is provided with a base part 800 formed of a piezoelectric material and having a predetermined length, and a pair of vibrating arms 700a, 700b extending side by side from the base part 800.
Both of the vibrating arms 700a, 700b are respectively provided with groove parts 720a, 720b formed on the principal surfaces (the obverse and reverse surfaces) so as to extend in the longitudinal direction of the vibrating arms, and at the same time, provided with two systems of electrodes 910, 920 formed on the principal surfaces and the side surfaces thereof and supplied with driving voltages.
Regarding formation of the electrodes 910, 920, the electrode material is deposited on the entire area of the piezoelectric vibrator element 600 including the inside of the groove parts 720a, 720b using an evaporation process or a sputtering process. Then, by removing the parts where the hatching does not exist in FIG. 6 using a photolithography process, the electrode 910 and the electrode 920 are separated from each other.
In the piezoelectric vibrator element 600 formed in such a manner as described above, by applying voltages different in system respectively to the electrode 910 and the electrode 920, both of the vibrating arms 700a, 700b vibrate relatively to each other.
Incidentally, the piezoelectric vibrator element 600 is miniaturized due to a requirement from an electronic apparatus in which the piezoelectric element 600 is mounted. Due to the miniaturization of the piezoelectric vibrator element 600, the width W0 in each of the vibrating arms 700a, 700b has also been narrowing.
Meanwhile, the distance W5 between the electrode 910 and the electrode 920 has previously remained in a range of 6 through 7 μm.
Therefore, there is a problem that the width w of each of the electrodes 910, 920 formed on the principal surfaces (the reverse and obverse surfaces) of each of the vibrating arms 700a, 700b narrows, and as a result, the area of the electrode part making a contribution to the vibration (where the piezoelectric effect is excited) decreases.
It should be noted that although it is also possible to narrow the width of each of the groove parts 720a, 720b as much as the decrease in the width W0 in each of the vibrating arms 700a, 700b, it is not preferable for the vibrating arms 700a, 700b with the width W0 equal to or smaller than 10 μm to narrow the groove part width since the CI value increases.